I believe* that the power supply inside the Large PS2's were just a 12V/5V supply. I'm not 100% sure though. I had to fix ours once as the PS2 was dropped from a high place and the power supply board...

Hello Dave. First of all, you have to ask yourself what you want the PC to do, functions etc. Once you have that figured out it's really a matter of selecting the hardware that can do what you want....